MEASUREMENT OF LONG TERM STRAIN IN FULL-SCALE EXPERIMENTAL CONCRETE SLABS

LONG TERM DIMENSIONAL CHANGES IN CONCRETE UNDER FIELD CONDITIONS HAVE BEEN OBSERVED BY MEASURING THE STATIC STRAINS IN REFERENCE SLABS LAID IN CONNECTION WITH FULL- SCALE EXPERIMENTAL REINFORCED CONCRETE ROADS ON A.1 AT ALCONBURY HILL, HUNTS., AND THE GRANTHAM BY-PASS, LINCS. AND THE PRESTRESSED CONCRETE ROAD ON A.46 AT WINTHORPE, NOTTS. THE RESULTS SHOW THAT THE CONCRETE TENDS TO SWELL AT FIRST, EXPANSION REACHING A VALUE OF ABOUT 150 MICROSTRAINS IN SOME CASES, AND THAT AFTER ABOUT 6 MONTHS THIS PROCESS IS REVERSED, AND CONTRACTION TAKES PLACE. SHRINKAGE IN CONCRETE OF THE ORDER OF 300 MICROSTRAINS WAS OBSERVED IN 10 YEAR OLD REFERENCE SLABS. APART FROM HAVING AN OVERALL SHRINKAGE THE REFERENCE SLABS ALSO DEVELOPED HIGH VERTICAL SHRINKAGE GRADIENTS (OVER 150 MICROSTRAINS IN A 225 MM SLAB), WHICH ARE THOUGHT TO CONTRIBUTE TO FAILURES IN ROAD SLABS. AT INTERVALS DURING THE FIRST TEN YEARS OF LIFE OF A SELECTED NUMBER OF THE REINFORCED CONCRETE SLABS ON A.1 AT ALCONBURY HILL, MEASUREMENTS WERE MADE OF THE HORIZONTAL STRAIN DEVELOPED CLOSE TO THE UNDERSIDE OF THE SLAB AND IN ITS CENTRAL AREA BY A LOADED LORRY STANDING WITH ONE PAIR OF ITS TWIN REAR WHEELS DIRECTLY ABOVE THE STRAIN GAUGE. THE RESULTANT STRAIN WAS OVER 50 PER CENT HIGHER IN A SLAB OF NORMAL STRENGTH THAN IN ONE OF HIGH COMPRESSIVE STRENGTH. A SLAB 150 MM. THICK GAVE GREATER STRAINS UNDER THE LORRY LOAD THAN WERE MEASURED UNDER ANY OF THE 200 AND 250 MM SLABS. VISUAL INSPECTION OF THE EXPERIMENTAL ROAD SHOWED THAT CRACKS FORMED AT A GREATER RATE IN THE 150 MM SLAB THAN IN THE THICKER SLABS. THE SURFACE LOADING TESTS ALSO SHOWED THAT, FOR THE CENTRAL AREA OF A CONCRETE SLAB, THE TENSILE STRAINS PRODUCED CLOSE TO THE UNDERSIDE BY VEHICLE LOADING ARE ALGEBRAICALLY ADDITIVE TO THOSE RESULTING FROM THERMAL WARPING DURING HOT AFTERNOONS. /RRL(A)/

  • Supplemental Notes:
    • Report No LR 259, 19 PP, 7 FIG, 3 TAB, 1 PHOT, 10 REF
  • Corporate Authors:

    Road Research Laboratory /UK

    ,    
  • Authors:
    • Potocki, F P
  • Publication Date: 1969

Subject/Index Terms

Filing Info

  • Accession Number: 00212988
  • Record Type: Publication
  • Source Agency: Road Research Laboratory /UK
  • Files: TRIS, ATRI
  • Created Date: Jun 11 1971 12:00AM